The present invention relates to a shield for tunneling and mining applications.
More particularly, it relates to a shield of the aforementioned type when a tool for removing material from the tunnel of a mine face (hereafter called the work face for convenience) is arranged in a work chamber of the shield.
Shields of this type constitute a screen which protects the workers and the material-removing equipment as material is removed from the work face, and the shield is pushed forward as the work advances. The shield may, as in the present invention, be cylindrical and include the entire tunnel section; in this case it has at the front a work chamber which is open at its leading end to the work face i.e. to the material to be removed, and which at its rear end is closed by a transverse wall behind which there is located a tunnel cladding, for example in the form of ring segments which are installed as the shield moves forward.
A shield of this general type is known from German Pat. No. 2,431,512. It has the material-removing equipment located in the working chamber and the working chamber itself is filled with a pressure medium in which the material-removing equipment works. The purpose of this pressure medium is to support the work face i.e. to prevent the material at the work face from crumbling or even collapsing if the mine gallery or tunnel is being driven through loose material, rather than through e.g. solid rock.
The prior-art shield is rather satisfactory; however, it has been found that it may become necessary for personnel to enter the work chamber at times. This necessity may arise if, e.g. some obstruction is encountered in the material of the work face which cannot be readily removed by the material-removing equipment, for example large rocks, tree trunks or parts of sunken habitations. If that occurs it is necessary, in the prior-art shield to remove the pressure medium e.g. a thixotropic liquid, before the workers can enter the chambers. With the removal of the pressure medium, of course, the protection against a possible collapse of the work face is removed with the result that during manual disengagement of the obstruction in question the danger exists that the work face might collapse and possibly cause injuries or even death among the workers in the work chamber.